In order to observe reflective objects, particularly metallic objects, it is common to use diffuse incident illumination to obtain a shadow-free image without highlights from light sources. Various devices for providing such diffuse illumination have been described in the prior art.
International Patent Publication WO 94/19908 describes an illumination device for providing diffuse incident illumination, in which a hemispherical translucent dome is illuminated from the outside to produce diffuse illumination in its interior. In International Patent Publication WO 01/16585 A1, an also hemispherical reflector is illuminated from below so as to produce diffuse illumination. Finally, in Japanese Patent Publication JP 56126705 A, a rotating mirror is provided in a hemispherical dome to produce diffuse incident illumination. All of these approaches have the inherent disadvantage that the domes can hardly be adapted to the different working distances required for different objectives (objective lenses).
In order to solve this problem, German Publication DE 20 2007 012 281 U1 teaches to attach a movable cover to the reflector. In this approach, the reflector is cylindrical in shape and is equipped with a light source in its cylindrical wall. This light source illuminates the inner cylinder wall, whereby light is reflected, thereby providing diffuse illumination of the object. The reflector is provided with a movable cover to take into account the different working distances associated with different objectives. This approach has the disadvantage that the cover must be fixed in position according to the working distance, which may hinder focusing and manipulation of the object. Moreover, a fixed clamping connection between the reflector and the cover may result in injury to the user, for example, during focusing of the object, and/or in damage to the reflector, the object, or the objective. In addition, the reflector is large in size and cumbersome to handle. The accessibility to the sample is greatly reduced.
Taking this prior art as a starting point, it is an object to provide an illumination device for a microscope, which produces diffuse incident illumination, is easily adaptable to different working distances, reduces the risk of injury to the user and the risk of damage to equipment, and which allows easy access to the sample and is easy to operate.
According to the present invention, there is provided an illumination device for a microscope having the features and advantageous embodiments described herein.